Alain Delon, the actor, is to be held for questioning for a further 24 hours by police who are investigating the murder near here last September of his former secretary and bodyguard, a young Yugoslav, Stefan Markovic. Delon, who has been interrogated three times before, underwent 12 hours of questioning yesterday.

Under French law, the normal period of 24 hours for which a witness can be held before a charge is preferred may be extended to 48 hours on the written authority of a Public Attorney.

Mavkovic's body was found inside a sack on a garbage dump.

He had been shot in the head several days earlier and beaten on the back of the skull to cover the bullet wound.

Public interest in the affair has two aspects. One, obviously, is the personality of the actor, a handsome man, aged 33, who will be familiar to British audiences for his performance in the film of the Liberation of Paris, "Is Paris Burning?"

After a disturbed and semi-delinquent adolescence, M. Delon served in the Navy in Indo-China, and after his return, had a period on the Marseilles waterfront, where, on his own admission, he made friends among the criminal world. He was "discovered" for the cinema when he came to Paris and began to frequent the night clubs. He has retained a taste for playing tough or criminal parts.

The second aspect concerns the circles in which M. Delon and his wife Nathalie have moved. Early inquiries revealed that Markovic was involved in a drug ring and that he organised parties at which the entertainment catered for somewhat specialised tastes.

Paris has been seething with rumours about the public figures, including leading politicians, who are said to have been involved in these parties, to have been photographed in compromising situations, or to have been threatened by Markovic, whose subsidiary activities were understood to have included blackmail.

The truth was that the young Yugoslav, like M. Delon and his wife, were prominent figures in "café society". This provides a common meeting ground for people ranging from politicians through artists and intellectuals, to the fringes of a fairly louche underworld.

Also held for questioning are the actor's impresario, M. Georges Beaume; his chauffeur, M. Marcel Gasparini; and a photographer who has been closely associated with him, M. Jean- Pierre Bonotte. Ten other people were also detained.

The one man against whom a charge of being implicated in the crime has so far been preferred is undergoing questioning at Versailles by the Examining Magistrate, M. Patard. He is M. François Marcantoni, a Corsican café proprietor who is a self-styled reformed criminal. M. Marcantoni is a long-standing friend of M. Delon.

[The actor was filming in St Tropez at the time of the murder in Paris and was never charged. He was suspected because Markovic had sent a letter to his brother saying: "If I get killed, it's 100% the fault of Alain Delon and his godfather François Marcantoni". Mercantoni was charged with accessory to murder and released after 11 months as his guilt could not be established.]